CODEWITHSUNDEEP
rmatrixcomparison
Jon Nelson
Jon Nelson

Reputation: 11

Replacing values in one matrix with values from another

I'm trying to compare to matrices. When the values aren't equivalent then I want to use the value from mat2 so long as it is greater than 0; if it is zero, then I want the value from mat1. As the code is currently, it appears to constantly return the value of mat1.

Here is my attempt:

mat.data1 <- c(1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 0, 1, 0, 1, 1, 0, 0, 1)
mat1 <- matrix(data = mat.data1, nrow = 5, ncol = 5, byrow = TRUE)


mat.data2 <- c(0, 0, 0, 0, 0, 0, 1, 2, 0, 0, 0, 1, 2, 2, 0, 0, 0, 1, 2, 2, 0, 2, 1, 0, 1)
mat2 <- matrix(data = mat.data2, nrow = 5, ncol = 5, byrow = TRUE)

mat3 = if(mat1 == mat2){mat1} else {if(mat2>0){mat2} else {mat1}}

the expected output should be

1   0   1   1   1
0   1   2   1   1
1   1   2   2   0
1   1   1   2   2
1   1   1   0   1

Upvotes: 1

Views: 44

Answers (2)

akrun
akrun

Reputation: 887951

We can use coalesce

library(dplyr)
out <- coalesce(replace(mat2, !mat2, NA), replace(mat1, !mat1, NA))    
replace(out, is.na(out), 0)

Or as @Axeman mentioned

coalesce(out, 0)

Upvotes: 2

mfidino
mfidino

Reputation: 3055

Here is one potential way to do it.

mat.data1 <- c(1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 0, 1, 0, 1, 1, 0, 0, 1)
mat1 <- matrix(data = mat.data1, nrow = 5, ncol = 5, byrow = TRUE)


mat.data2 <- c(0, 0, 0, 0, 0, 0, 1, 2, 0, 0, 0, 1, 2, 2, 0, 0, 0, 1, 2, 2, 0, 2, 1, 0, 1)
mat2 <- matrix(data = mat.data2, nrow = 5, ncol = 5, byrow = TRUE)


mat3 <- mat1
to_change <- which(mat2 != mat1 & mat2 > 0)
mat3[to_change] <- mat2[to_change]

This specific use of which essentially asks for the locations in mat2 that are not equal to that in mat1 AND where mat2 is greater than zero. You can then just do a subset and place those values in mat3.

This output is then:

> mat3
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    0    1    1    1
[2,]    0    1    2    1    1
[3,]    1    1    2    2    0
[4,]    1    1    1    2    2
[5,]    1    2    1    0    1

Upvotes: 2

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